Researchers at the Hospital for Special Surgery, New York, N.Y. (the assignee of the present invention) have been working for many years on the development of prosthetic joints, including the knee joint. Developments in prosthetic knee joints have come to focus on "total" prostheses in which all contacting surfaces of the femur and tibia are replaced by surfaces of the femoral and tibial components of the prosthesis and on "stabilized" prostheses in which parts of the components, such as hinge pins or balls and sockets, control the motion. In general, the total knee prostheses currently used allow antero-posterior translation, lateral angulation and rotation in much the same way as the anatomical knee joint does and rely on the tendons and ligaments to impart stability. In some cases, however, the soft tissue is inadequate for one reason or another to provide the required stability, and the prosthesis is highly subject to dislocation and therefore of impaired usefulness in restoring normal function.
Hinge and ball and socket type knee joint prostheses generally fail to reproduce the motions of the anatomical joint. For that reason, they are not considered desirable, except for patients having inadequate soft tissue in the knee joint to provide stability, because normal function is not restored--the joint functions abnormally. Moreover, reliance on the mechanics of the prosthesis for stability places considerable strain on the prosthesis, and failure by dislodgment of the components is much much more prevalent with stabilized prostheses than with total prostheses.
U.S. Pat. No. 4,213,209 issued July 22, 1980 for "KNEE JOINT PROSTHESIS" (owned by the assignee of the present invention), describes and shows a knee joint prosthesis which can be characterized as a hybrid of the total and stabilized types. It has the attribute of providing generally normal function characteristic of total prostheses and the attribute of limiting certain excessive relative motions characteristic of stabilized prostheses.